Silicon carbide (SiC) is a semiconductor material with a larger band gap and a greater dielectric breakdown field strength, compared to silicon (Si), and is therefore expected to be applied to next-generation low-loss power devices, etc. SiC includes various types of SiC, such as 3C—SiC (cubic system SiC), 6H—SiC (hexagonal system SiC) and 4H—SiC.
One of typical switching elements among power devices using SiC is a field effect transistor, such as a metal insulator semiconductor field effect transistor (hereinafter abbreviated as a “MISFET”) or a metal semiconductor field effect transistor (hereinafter abbreviated as a “MESFET”).
In such a switching element, the ON state in which a drain current of several amperes (A) or more flows and the OFF state in which the drain current is zero can be switched by a voltage applied between a gate electrode and a source electrode. Further, in the OFF state, the device can withstand a high voltage of several hundred volts (V) or more.
To make much higher current flow in the power device such as a MISFET, an increase in an integration density of the device is effective. Thus, vertical power MISFETs having a trench gate structure as a substitute for a conventional planar gate structure have been suggested. In the MISFET having the trench gate structure, a unit cell area can be reduced since a channel region is formed on a sidewall portion of a trench formed in a semiconductor layer. As a result, the integration density of the device can be increased.
Patent Document 1 discloses a method for reducing differences in plane orientation between both sidewalls of a trench by using a substrate with a small off-angle of equal to or larger than 0.3° and smaller than 4°, and preferably equal to or smaller than 1°.
Patent Document 2 discloses a method for reducing an effective off-angle approximately in half by forming a trench in a direction which forms an interior angle of 30° relative to the off direction.